Vascular disease risk is high in diabetics, in those with impaired glucose tolerance, and in the obese. Reduction of atherosclerosis and vascular complications in the large mass of persons with these conditions is a major medical and public health challenge. Because energy balance and habitual exercise are so intimately related to these processes, and because many theoretic and some demonstrated effects of exercise are anti-diabetogenic and anti-atherogenic, it is proposed to study systematically the effects of regular exercise in latent and frank diabetics. This application concerns the specific study of effects on glucose and lipid metabolism of regular walking at two different intensities, durations, and frequencies. Fifty pre-diabetic or mild maturity-onset diabetic men being managed with diet alone will be randomly assigned 12 week walking programs on a treadmill for either 30 or 60 minutes, 3 or 5 times a week, at one of two intensities equivalent to 40% or 60% of their functional aerobic capacity as demonstrated by exercise testing. The effects will be determined on body composition, glucose tolerance, plasma insulin and glucagon levels, and blood lipids including high density lipoprotein. The duration and the independence of effects of chronic exercise will be studied during and after the training period. The significance of this study is to evaluate the potential value of habitual regular exercise in prevention, attenuation, and management of the diabetic state, and to learn about the intensity, duration and frequency necessary for a given metabolic effect.